I think you might be underestimating the scale of the attack. The amount of payroll money alone.... How many people would you need to put on the payroll and for how much money?
Some Bitcoin Core devs are already on payrolls of Bitcoin service providers (Blockstream being probably the most well-known example). When we talk about developer influence on the public opinion in the community, then quality -- i.e. that these devs are "respected voices" -- is also more important than quantity.
I don't see it that way. Without real authority over Bitcoin, popular devs are just members of the top influencer club. And their values must align with the values of Bitcoin. Otherwise it would be like running for president of the US while wearing a North Korean flag pin. I think if devs want to stay popular, they do what the community wants.
There isn't such a "number" or "limit". All decentralized systems can eventually degenerate. Bitcoin has however fortunately a quite good balance between powers, so the probability of a successful attack is much lower than it was in Ethereum where the rollback finally occured quite fastly.
I mean the amount of effort it would take to attack Bitcoin is much different than the amount of effort it would take to attack some random altcoin (based on a clone btc blockchain). And even then, the damage would be reversible.
The more decentralized something is, the more secure it becomes.